The present invention relates to the field of mass-storage devices. More particularly, this invention relates to a method and apparatus for reducing acoustic noise from disc drives.
Devices that store data are key components of any computer system. Computer systems have many different devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, and circuitry that is used to write and/or read data to and from the disc via the transducer. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil (or xe2x80x9cwrite headxe2x80x9d) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or xe2x80x9cread headxe2x80x9d) that detects changes in the magnetic field along the tracks for reading data.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
When the disc assembly is rotated at high speed, the air adjacent to the spinning disc or discs is caused to move as well. This moving air moves between the rotating disc and the read/write transducer, creating an air bearing, and advantageously causing the transducer to xe2x80x9cflyxe2x80x9d over the disc surface.
An operating disc drive can emit relatively large amounts of acoustic noise generated by vibrations of the disc drive cover caused by the spinning motions of the spindle and seek and track following motions of the actuator. The spindle and actuator movements create forces that act on the structure of the disc drive. These forces eventually find a path to the device enclosure. When the forces reach the device enclosure, the forces are converted into displacements which in turn create pressure waves in the surrounding air which are perceived as acoustic noise to the human ear.
The actuator assembly moves in response to energizing a voice coil motor to move the actuator assembly about a pivot axis, thereby swinging each of the arms associated with the actuator assembly, the load springs, and associated read/write head over the associated disc surface. When moved in this manner during normal operation, the assembled load springs and associated read/write head tend to vibrate at some frequencies. The spindle motor, and rapidly spinning the discs, contribute additional vibration. Vibration from the spindle motor and voice coil motor actions may be transmitted to the disc drive housing through the pivot and spindle journals. The resulting vibration in the housing causes radiation of acoustic noise, especially from the cover. Such acoustic noise may be annoying and may suggest poor quality to the user.
The device enclosure actually acts like a speaker for the internal forces created by the spindle and actuator movement. The dynamics of the device enclosure, such as the natural modes of vibration, act as mechanical amplifiers for the forces generated inside the drive. It has been found that the shape of the acoustic spectrum in the frequency domain is similar to the shape of the mechanical transfer function of the device enclosure. If it were possible to make the device enclosure infinitely stiff then no displacements could be created that would be manifested as acoustic noise.
In addition to being annoying and possibly suggesting poor quality to the user, high acoustic emissions from disc drives tend to reduce the comfort level for a particular computing environment. As a result, acoustic noise emanating from a disc drive is a critical performance factor that is usually tightly specified to be below a maximum level. As part of the quality assurances practices when manufacturing disc drives, the drives are tested in an acoustic tester to determine the amount of noise emanating from the device. Drives that emit noise above a maximum threshold need to be re-worked to be in compliance with the requirements.
Government agencies throughout the world are now requiring that the decibel level of average sound energy emanating from office equipment be substantially reduced. Computer manufacturers are also placing acoustic emission standards on disc drive manufacturers. Manufacturers of disc drives have also long recognized that certain improvements for data storage performance in disc drives, namely, to increase disc rotation velocity and to increase head actuator movement frequency, contribute to unwanted acoustic noise. There is a marked decrease in human sensitivity to acoustic noise below about 200 Hz and above about 6000 Hz. Thus, it is clearly advantageous to attenuate acoustic noise radiated from disc drives in the frequency range from about 200 Hz to about 4000 Hz.
Several methods to reduce the intensity of unwanted acoustic noise have been attempted. Among the several methods are the use of external dampening techniques for the entire disc drive. For example, mechanically isolating the cover of a disc drive from the mechanical reinforcement structure with a continuous airspace. Many designers believe that most of the unwanted acoustic frequencies emanate from a xe2x80x9cdrum-likexe2x80x9d top cover and from the base plate of the disc drive. Some designers have made strides in addressing the acoustic frequencies that escape from the top cover. The designers use cover dampeners and adhesives with inherent dampening properties on the cover. Other designers have attempted to completely surround the exterior of the disc drive with sound deadening material. Still other designers have attempted to completely isolate the spindle from the base in order to reduce the unwanted acoustic emissions at multiple frequencies. Such spindle isolation conventionally includes indirect attachment of the spindle to the base. Many environments where disc drives are used are sensitive to the amount of acoustic emissions (or noise) coming from an operating disc drive.
Disc drives are now being contemplated for use in home entertainment applications. Use of disc drives is now contemplated for video and television. One application of disc drives includes adding them to home set top boxes. Still others use disc drives to capture images from television for replay at a later time. One such system is the TiVo System from Phillips Corporation. Users in the home entertainment area are especially sensitive to acoustic noise, since noises seem more pronounced during quiet scenes of a movie or when background music is softly played.
Therefore, it is desirable to reduce such acoustic noise. What is also needed is a simple solution that is not prohibitively costly and which introduces few, if any, new parts to the disc drive. What is needed is a method and apparatus to substantially reduce unwanted acoustic emissions at or near the spindle. Also needed is an inexpensive method and apparatus which only slightly increases the complexity of the manufacturing processes needed to manufacture the drive. The solution also must not increase the size of the disc drive system. Clearly, there is a need for a solution to reduce or eliminate the vibration energy transferred to the cover and housing from the voice coil and spindle motors. There is also need for a solution which minimizes re-working of disc drives.
A disc drive includes a base plate and a spindle attached to the base plate. In addition, at least one disc is attached to the spindle and the spindle is adapted to rotate with respect to the base plate. The disc drive also includes a cover for attaching to the base plate. The cover and the base plate form a disc enclosure which encloses the at least one disc and a portion of the spindle. The disc enclosure has an interior and an exterior. At least a portion of the interior surface of the disc enclosure is provided with anechoic features. In one embodiment, the anechoic features are formed integral to the cover and are covered with a energy-absorbing material. In another embodiment, the anechoic features are formed integral to the base plate and are covered with a energy-absorbing material. In another embodiment, the anechoic features are formed integral to both the base plate and to the cover and each is covered with a energy-absorbing material.
In still another embodiment, the anechoic features are formed on a liner which is attached to at least a portion of the interior surface of the disc enclosure. The liner is formed from an energy-absorbing material and attached to the interior surface of the cover, or to the interior surface of the base plate, or to both the cover and base plate. The liner portions are attached to at least a portion of the interior surface of the disc enclosure. The anechoic features are formed to attenuate a selected range of frequencies. In some embodiments, the anechoic features are V-shaped rows while in other embodiments the anechoic features are spike-shaped. The V-shaped rows may be orientated in different directions on the interior surface of the disc enclosure.
A method for substantially reducing vibrations from a disc drive system having a base plate and a cover which form a disc enclosure having an interior surface and an exterior surface includes the steps of providing anechoic features on the base plate corresponding to the interior surface of the disc enclosure, and providing anechoic features on the cover corresponding to the interior surface of the disc enclosure. One embodiment of the method may further include the steps of forming a liner member for the base plate of a disc drive, attaching the liner member to the base plate, forming a liner member for the cover of a disc drive, and attaching the liner member to the cover. Another embodiment of the method may further include the steps of forming the base plate of a disc drive with anechoic features therein and placing an energy-absorbing material on the base plate, and forming the cover of a disc drive with anechoic features therein, and placing an energy-absorbing material on the cover.